Moore, Paul B. Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois.
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A mineral with chemical composition BaSO4. It is isostructural with celestite, SrSO4, and anglesite, PbSO4. Barite is orthorhombic, space group Pnma, a = 0.887 nanometer, b = 0.545 nm, c = 0.714 nm. The illustration shows typical crystals. Barite possesses one perfect cleavage, and two good cleavages as do the isostructural minerals. Anhydrite, CaSO4, although also orthorhombic, possesses a different space group and a different structure. Solid solution in the series BaSO4–SrSO4 occasionally occurs in the natural environments. Solid solution in BaSO4–PbSO4 is uncommon, although up to 30 mole % PbSO4 in barite has been reported. Infrequency of natural solid solution between these two end members may stem from the different origins of the two minerals, anglesite being an oxidation and weathering product of galena ores. Since Ba2+ has the largest ionic radius of the isostructural series with the ionic radius of , separation of these species may be a consequence of this geometrical distinction. Barite can be distinguished from celestite and anhydrite by its superior specific gravity of approximately 4.5. The mineral is relatively soft, approximately 3 on Mohs scale. The color ranges through white to yellowish, gray, pale blue, or brown, and a thin section is colorless. Barite is often an accessory mineral in hydrothermal vein systems, but frequently occurs as concretions or cavity fillings in sedimentary limestones. It also occurs as a residual product of limestone weathering and in hot spring deposits. It occasionally occurs as extensive beds in evaporite deposits.
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